The best replacement for polystyrene is polypropylene.

The best alternatives to polystyrene are rated as following:
★★★★★  polypropylene
★★★★  polyurethane
★★★  styrofoam
★★  polyethylene
★★  polyurethane insulation
★★  polyisocyanurate
★  polyurethane garage door
★  celotex
★  paper
★  plaster coving
★  polycarbonate
★  rockwool
★  kingspan
★  polypropylene tubes
★  polyurethane garage doors
★  polyethylene foam
★  expanded polystyrene
★  styrene
  extruded polystyrene
  mineral wool
  polyiso
  fiberglass insulation
  urethane
  extruded
  expanded polypropylene
  expanded polyurethane

Your alternative for polystyrene is not listed? Suggest!
Speaking about polystyrene, one probably shouldn't forget about adhesive.

Other search terms related to polystyrene and their ratings are:
★★★★★ adhesive
★ plasterboard
You have in mind a companion for polystyrene and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of polystyrene in all years. Click on graph for more.
polystyrene
polypropylene
polyurethane